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The 41-year-old boxing legend was part of a shocking announcement on Monday in Japan as he was introduced at a Rizin Fighting Federation press conference in Tokyo, Japan, where officials declared that Mayweather will step into the Rizin ring opposite 20-year-old kickboxing and MMA sensation Tenshin Nasukawa at a year-end show on Dec. 31.

BJPenn.com and MMA Sucka were first to report the news of Mayweather’s involvement and Mayweather himself teased the announcement earlier on Instagram:

Before Nasukawa was introduced, Rizin promoter Nobuyuki Sakakibara provided a brief explanation for why a partnership with Mayweather makes sense.

“I think my shortest answer to that is the fact that now we are aligned to achieve something together and that is hitting a new challenge, taking a step forward to whatever wonderful thing that we can create together,” Sakakibara said via a Japanese translator.

For his part, Mayweather was on the same page. He expressed great enthusiasm over getting the chance to visit Japan more regularly and promote fighters from his Money Team in the country, and said that he plans to continue working with Rizin in the future.

“Rizin has done a remarkable job with the fighters,” Mayweather said. “I look forward to giving you guys entertainment come December 31, but my relationship with Rizin, it doesn’t stop just here. I look forward to taking this worldwide.”

Nasukawa, 27-0 as a kickboxer and 4-0 in MMA, sounded confident that his fight with Mayweather would draw a strong viewership.

“I would probably say that this is my biggest event in life, so far,” Nasukawa said, via a Japanese translator. “And I’m very happy that this is going to materialize.”

“Nobody has defeated my opponent in the past,” he continued, referring to Mayweather’s 50-0 pro boxing record. “And I would like to be the man who makes history. My punch can change the history and I will show that to you, so please stay tuned.”

It was not announced exactly what kind of fight Mayweather and Nasukawa would be participating in. Sakakibara could only say that the contest was going to be under “special rules,” but otherwise gave no indication whether it would skew more towards boxing, kickboxing, or MMA. The weight class that the fighters will be competing in was also not mentioned.

Mayweather was last seen putting ending a two-year retirement to take on then-UFC champion Conor McGregor in a heavily-hyped crossover boxing bout in August 2016 that Mayweather would win by 10th-round TKO. He has since teased the possibility of competing in MMA.

Nasukawa is coming off of a crossover bout of his own. At Rizin 13 in September, he defeated bantamweight star and one-time UFC flyweight title challenger Kyoji Horiguchi in a three-round kickboxing match.

“My opponent looks taller than he actually is and I think that comes from the aura that he has, but I think I can hit him,” Nasukawa said.

Rizin 14 is expected to take place at the Saitama Super Arena in Saitama, Japan.